Besides cast aluminum, you can TIG weld a multitude of metals, including stainless steel, billet or extruded aluminum, cast iron, nickel, magnesium, copper, and titanium. And with the right alloy filler, you can even join dissimilar metal types, like cast iron and steel.
Cast aluminum welding repairs can be tricky.
For the most part, the level of difficulty depends on the service environment the part was subjected to.
For example, aluminum can be exposed to fresh water, salt water, exhaust gas carbon, oil, and other nasty things.